For some communication networks during the transfer of packets between a plurality of nodes of the network, the receiving node does not have the capability to look at the payload of a received packet, for example, an optical transport network (OTN). The traffic generated by the routers of such networks, typically 10 Gigabit Ethernet and 100 Gigabit Ethernet, is transported over the OTN via transponders. The transponders encapsulates the data into Optical Channel Data Unit-k (ODUk) containers for transporting the packets, for example 10 GE is encapsulated to ODU2e container and 100 GE is encapsulated to ODU4 container suitable for the transport over Dense Wavelength-Division Multiplexing (DWDM) links.
The optical nodes of the OTN comprise optical cards that are not able to look at the payload received on their client interfaces for example client interfaces Synchronous Digital Hierarchy (SDH), Constant Bit Rate (CBR), Storage Area Network (SAN), for example when the transponder client is packet like layer 3 Internet Protocol (IP) or layer 2 Ethernet.
Furthermore such communication networks are required to provide communication control between the nodes (e.g. router and optical nodes). This may be achieved by means of out of band control channels or in band control channels. Out of band control channels, however, are extremely complicated from an operational and maintenance view point and many changes in the router behavior is required. Moreover it is not suitable for operations related to the physical link, for example auto-discovery, link failure etc. In band control channels are difficult to implement in a communication system in which the receiving node has limited packet inspection capability.
An example of an optical transport system in which a router directly communicates with an optical node is shown in FIG. 1. The optical transport system comprises a router 101 comprising a data card 105 in communication with a transponder 107 of an optical node 103. Data packets received at the optical node 103 are passed through a passive filter 109 to one of plurality of Wavelength Selective Switch (WSS) units 111_1 to 111_n for output across the network via corresponding optical amplifiers 113_1 to 113_n. The direct communication between the router 101 and optical node 103 is activated using any L2 and L3 protocols having no split between the control plane and the forward plane. The optical node 103 provides only transparent mapping of packets onto the OTN frame, thus the optical node has no packet processing or peer interface detection capability.
As a result, the only action allowed to the transponder 107 of the node 103 is to inject a maintenance signal into the container of a packet instead of the client as a consequence of a fail condition (e.g. Loss of Signal (LOS) of the Ethernet client detected by the transponder). The rules for mapping the packets onto the network and the action to inject a maintenance signal are specified by ITU-T G.709 and G.798. Considering the above limited capability in inspecting packets, such transponders are not able to decode in-band control-plane packets. Therefore it is not possible to have a communication between the router and the transponder unless via network management system and controller units. This is a limitation because many control plane protocols use in-band packets to connect nodes, cards, etc.